The development was really fast. After announcing they had the new administration interface publicly available I was eager to start upgrading this website right away... and so I did! The Version you are viewing now runs on the latest eZPlatformV2 kernel and everything!
The new interface is really nice and I would recommend you switch as soon as possible! If you are extending the YUI-base interface, you know how hard it actually gets. Complications like in the old interface are just a thing of the past (expecting you know your way around symfony that is).
My first impression of the new interface was "Finally a fast interface I can easily extend", not even knowing how amazing it was to extend!
And at that point (without even having a RC) I started working on my first bundles extending the new interface. Most of them mainly to check what I can do and if there are any limitations. Let me tell you, that I have not found any at this point!
My bookmark-bundle is currently in it's beta phase and publicly available here. Note that this bundle is currently in beta and hosted on my private gitlab server. Though you will be able to install it (the repository is public).
I can emphasize enough that you should upgrade asap.
Afaik studio should also be available withing the two upcoming months (though I'm only using it at work).
Check out the release description too!